From: Al Viro <viro@zeniv.linux.org.uk>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Greg KH <gregkh@linuxfoundation.org>,
yu kuai <yukuai3@huawei.com>,
rafael@kernel.org, oleg@redhat.com, mchehab+samsung@kernel.org,
corbet@lwn.net, tytso@mit.edu, jmorris@namei.org,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
zhengbin13@huawei.com, yi.zhang@huawei.com,
chenxiang66@hisilicon.com, xiexiuqi@huawei.com
Subject: Re: [PATCH 1/3] dcache: add a new enum type for 'dentry_d_lock_class'
Date: Fri, 15 Nov 2019 14:17:54 +0000 [thread overview]
Message-ID: <20191115141754.GR26530@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20191115085805.008870cb@gandalf.local.home>
On Fri, Nov 15, 2019 at 08:58:05AM -0500, Steven Rostedt wrote:
> On Fri, 15 Nov 2019 13:48:23 +0000
> Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> > > BTW, what do you mean by "can debugfs_remove_recursive() rely upon the
> > > lack of attempts to create new entries inside the subtree it's trying
> > > to kill?"
> >
> > Is it possible for something to call e.g. debugfs_create_dir() (or any
> > similar primitive) with parent inside the subtree that has been
> > passed to debugfs_remove_recursive() call that is still in progress?
> >
> > If debugfs needs to cope with that, debugfs_remove_recursive() needs
> > considerably heavier locking, to start with.
>
> I don't know about debugfs, but at least tracefs (which cut and pasted
> from debugfs) does not allow that. At least in theory it doesn't allow
> that (and if it does, it's a bug in the locking at the higher levels).
>
> And perhaps debugfs shouldn't allow that either. As it is only suppose
> to be a light weight way to interact with the kernel, hence the name
> "debugfs".
>
> Yu, do you have a test case for the "infinite loop" case?
Infinite loop, AFAICS, is reasonably easy to trigger - just open
a non-empty subdirectory and lseek to e.g. next-to-last element
in it. Again, list_empty() use in there is quite wrong - it can
give false negatives just on the cursors. No arguments about
that part...
next prev parent reply other threads:[~2019-11-15 14:18 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-15 3:27 [PATCH 0/3] fix potential infinite loop in debugfs_remove_recursive yu kuai
2019-11-15 3:27 ` [PATCH 1/3] dcache: add a new enum type for 'dentry_d_lock_class' yu kuai
2019-11-15 3:27 ` Greg KH
2019-11-15 4:12 ` Al Viro
2019-11-15 7:20 ` Greg KH
2019-11-15 10:08 ` yukuai (C)
2019-11-15 13:16 ` Al Viro
2019-11-15 13:38 ` Steven Rostedt
2019-11-15 13:39 ` Steven Rostedt
2019-11-15 13:48 ` Al Viro
2019-11-15 13:58 ` Steven Rostedt
2019-11-15 14:17 ` Al Viro [this message]
2019-11-15 17:54 ` Al Viro
2019-11-15 18:42 ` [RFC] simple_recursive_removal() Al Viro
2019-11-15 19:41 ` Al Viro
2019-11-15 21:18 ` Al Viro
2019-11-15 21:26 ` Steven Rostedt
2019-11-15 22:10 ` Al Viro
2019-11-16 12:04 ` Greg KH
2019-11-17 22:24 ` Al Viro
2019-11-18 6:37 ` Greg KH
2019-11-15 10:02 ` [PATCH 1/3] dcache: add a new enum type for 'dentry_d_lock_class' yukuai (C)
2019-11-15 3:27 ` [PATCH 2/3] fs/libfs.c: use 'spin_lock_nested' when taking 'd_lock' for dentry in simple_empty yu kuai
2019-11-15 3:27 ` [PATCH 3/3] debugfs: fix potential infinite loop in debugfs_remove_recursive yu kuai
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